Buchner funnels are used in the laboratory for vacuum-assisted liquid filtering. They are traditionally made of porcelain, but are also available in glass and plastic versions.
Buchner funnels consist of an open straight-sided cylindrical chamber that narrows to a tube- or pipe-shaped opening. The tube-like extension can be placed through a stopper, which is then placed into the top of a filtration or Buchner flask. Plastic versions may have a bung hole located at the side of the chamber to which a vacuum may be attached. Buchner funnels are reusable.
The bottom of the Buchner funnel chamber may be perforated or contain a separate fritted disc. Filter paper is used for Buchner funnels with perforated lower surfaces. Place the filter paper of the preferred porosity inside the chamber, pre-wet, add the liquid, and apply the vacuum.
Funnels with fritted glass discs do not require filter paper. The fritted glass will be porosity-rated as fine, coarse, medium, etc. Filtration with a Buchner funnel proceeds more quickly than letting the liquid flow simply using gravity. Most Buchner funnels are also rated for a maximum vacuum pressure.
Buchner funnels are used in organic chemistry to help collect recrystallized compounds because it helps to remove moisture from the final product.
These funnels were named for their inventor, industrial chemist Ernst Büchner.